1. Field of the Invention
The present invention relates to a heat retentive food tray, and particularly a heat retentive food tray adapted to be heated by electrical induction. More particularly, the present invention relates to a heat retentive food tray with a cover, adapted to be heated by electrical induction.
2. Description of Related Art
In environments where food is prepared and cooked in a central location and distributed and served to consumers who are remotely located, such as, in hotels, aircraft and institutional settings, e.g., hospitals and nursing homes, there is often a delay between the time that the food is prepared, cooked and subsequently placed on a plate or other serving dish, and the time that the food is eventually presented to the consumer for consumption at a remote location. Accordingly, by the time the food is presented to the consumer, the food can become cold unless special measures are taken to keep the food hot. Various approaches to such meal service problems encountered in service environments, sometimes referred to as xe2x80x9csatelliting,xe2x80x9d have been employed in the food service and container industries.
One particular embodiment of heat retentive servers can be designed to support dishware, which in turn holds a portion of a meal that is to be kept hot. In such circumstances, the base is commonly called a xe2x80x9cpelletxe2x80x9d base, and the entire system, i.e., the base, dome and plate, is referred to as a xe2x80x9cpellet system.xe2x80x9d When a heat sink is incorporated into a server base and the base supports a food-carrying dish, or plate, the base can be referred to as a plate warmer.
In general, heat retentive servers employ convection or conduction heating in order to either heat a food service dish or heat a heat storage battery during food service operations.
U.S. Pat. No. 3,916,872 to KREIS et al., issued Nov. 4, 1975, discloses a heat storage dish comprising a central heat storage disk and an insulating member that surrounds the heat storage dish. The heat storage dish consists of a substantially circular metallic body member that may be equipped with a central opening. The heat storage dish may, for example, be heated by subjecting it to a high frequency field, thus inductively heating the heat storage dish. U.S. Pat. No. 3,557,774, issued Jan. 26, 1971 to KREIS, discloses a heat storage dish having a heat storage plate enclosed between an interior wall and an exterior wall, secured at their edges to prevent the entry of any external substance.
U.S. Pat. No. 4,776,386 to MEIER, issued Oct. 11, 1988, discloses an apparatus for cooling, storing and reheating food, using induction heating. This system includes a tray distribution system wherein a tray, which may be adapted to support, e.g., a soup tureen, a dish for meat, a hot beverage cup, a salad plate, and/or a similar plate such as a fruit dish, as well as a trough for cutlery, may be provided. A meal, supported on such a tray, can be stored in a refrigerated environment. In this system, the refrigerated cabinet in which the trays are stored includes induction coils. In practice, prior to serving, the cooling system of the refrigerator is turned off and the induction coils are activated to supply heat to the appropriate areas in the tray. U.S. Pat. No. 4,881,590 to MEIER, issued Nov. 21, 1989, discloses a similar system.
U.S. Pat. No. 3,734,077 to MURDOUGH et al., issued May 22, 1973, discloses a server that includes a recess in order to receive a plate. The server comprises an upper shell, a lower shell, a heating pellet and a resilient pad. The pad occupies the space between the under surface of the pellet and the lower shell and performs an insulating function, in addition to directing heat from the pellet in an upward direction rather than downwardly or laterally.
Each of the forgoing systems suffers from disadvantages. For example, systems which employ convection or conduction heating to preheat a food service container prior to employing the food service container to support, e.g., a dish having a food portion which is to be kept hot, require long xe2x80x9clead timesxe2x80x9d prior to being capable of being effectively used. Thus, such systems require relatively long periods of time in order to preheat the convection systems or other ovens used with said systems and in order to store enough heat in a heat sink or other heat storage means before the container can be usefully employed to keep foods warm in food service environments. Such lead times are undesirable and are typically on the order of about 60 to about 90 minutes and sometimes even longer, prior to the start of delivery or serving of the food to individual consumers.
Such food service containers including heat retentive servers and the like, suffer from other disadvantages. For example, heat retentive servers possess the disadvantage that the entire server can become hot and difficult to handle safely. Additional disadvantages include the fact that heat retentive servers which act as a heat sink, e.g., which employ a heat storage mass, tend to liberate heat in all directions. However, it is preferable to direct the heat which is liberated from the heat storage mass such that the heat is liberated substantially only within the heat retentive server itself, i.e., that portion of the heat retentive server which is enclosed by the bottom portion, side walls and dome or lid of the server. To achieve such an object, it is preferable to direct the heat given up by the heat storage mass such that the heat is directed upwardly.
U.S. Pat. No. 5,786,643 to Wyatt et al. is directed to a transportable heat retentive server, which includes a disk-shaped central portion having a disk-shaped heat storage disk. The ""643 Wyatt et al. server design does not have heat retention times comparable to the present invention.
The present invention is distinguished from the above-described bases because the heat storage disk is embedded within a tray on which a plate sits. The present design requires minimal storage space, has less pieces to wash and dry, the system is lighter and further, there is no need for a base dolly. Surprisingly, the heat retention performance for the present tray system is improved by about 61% when compared with conventional heat retentive bases wherein the heat storage disk is stored in the base rather than the tray according to the present invention.
The present invention provides a heat retentive tray system including a tray that is adapted to be inductively heated and to also store heat via a heat sink disposed directly within the tray so as to keep hot foods hot. Further, the heat retentive tray system includes a dome portion, which is thermally disposed about a top surface of the tray such that it completely covers a housing for a heat sink, thereby providing additional heat retention.
The present invention also provides an inductively heated heat storage member which can be rapidly heated and ready for use in serving individual hot portions to individual consumers, in such fashion that a large number of such heat retentive trays can be xe2x80x9cchargedxe2x80x9d, and plated with food in mass production fashion, while maintaining the food at least 140xc2x0 F. for more than 60 minutes.
The present invention also provides a heat retentive serving tray or the like, which can be heated by induction heating to keep selected foods hot. The serving tray includes a metal portion (i.e., a heat storage disk) that is heated to a predetermined temperature in response to electrical or electromagnetic induction, e.g., by induction heating. The metal layer is preferably centrally located and embedded within a tray and preferably circular, but can be positioned in various locations and comprise other than a circular shape. Further, the location of the disk within the tray can be such that the disk is thermally isolated from the remainder of the structure of the tray, such that heat is not conducted to the remainder of the tray, such as, by using a thermal break or insulation. For example, a thermal break is preferably incorporated as part of an expansion joint located between the heat storage mass and peripheral portions of the heat retentive tray, and insulation is preferably provided in bottom portions thereof.
Additionally, the heat retentive tray system can further comprise an upper cover or dome, wherein the upper cover and the top surface of the tray can cooperate to define an insulated volume. Preferably, the upper cover is disposed about the top surface of the tray or top shell.
The present invention provides a heat retentive tray having an upper surface, a recessed portion disposed in the tray and a heat storage member. The heat storage member is capable of being heated by induction and is disposed within the recessed portion. A portion of the upper surface that is disposed above the heat storage member can be flat. The recessed portion can be adapted to direct heat upward from the heat storage member through the upper surface. The tray can further have a top member and a bottom member that are disposed substantially adjacent to each other to form the recessed portion. The top member and the bottom member can be secured to each other by an ultrasonic annular weld. The tray can further have a fastening ring that is disposed adjacent to the top member and the bottom member for securing the top member to the bottom member. The tray can further have an expansion joint. The tray can further have a thermal break between the bottom member and the fastening ring. The tray can further have an annular cavity between the bottom member and the fastening ring, and the thermal break can be an o-ring disposed in the annular cavity. The heat storage member can be circular. The heat storage member can be centrally located in the tray. The heat storage member can have a plurality of holes disposed therein.
Additionally, the present invention provides a heat retentive tray system having a tray having an upper surface, an inner volume and a heat storage member which is capable of being heated by induction. The heat storage member is disposed in the inner volume. A portion of the upper surface that is disposed above the beat storage member can be flat. The heat retentive tray system also has a cover that is removably disposed on the portion of the upper surface above the heat storage member to form an insulated volume. The cover can have an inner wall, an outer wall and a space therebetween. The space can be at least partially filled with insulation. The inner volume can be adapted to direct heat upward from the heat storage member to the insulated volume. The cover and the upper surface can contact each other at a contact area wherein the heat from the heat storage member rises past the contact area. The tray can further have a top member and a bottom member that are disposed substantially adjacent to each other to form the inner volume. The top member and the bottom member can be secured to each other by an ultrasonic annular weld. A fastening ring can be disposed adjacent to the top member and the bottom member for securing the top member to the bottom member. The tray can further comprise an expansion joint. The tray can further have a thermal break between the bottom member and the fastening ring. The tray can also have an annular cavity between the bottom member and the fastening ring wherein the thermal break is an o-ring disposed in the annular cavity. The heat storage member can be circular. The heat storage member can be centrally located in the tray. The heat storage member can have a plurality of holes disposed therein.
The present invention further provides a method of serving food product to a plurality of consumers using the following steps:
A. subjecting a heat retentive tray comprising a substantially planar upper surface, an inner volume and a heat storage member that is susceptible to electrical induction heating and is disposed in the inner volume of the tray, to an electromagnetic field sufficient to inductively heat the heat storage member;
B. placing a quantity of food product which is disposed on a plate, onto the heat retentive tray above the heat storage member;
C. covering the tray, the inner volume where the heat storage member is disposed, the plate and the food product with an insulated cover which defines an insulated volume between the insulated cover and the tray so that ambient atmosphere does not come into contact with the plate and the food product; and
D. serving the food product to at least one of a plurality of consumers.